Nanopump devices and methods

Abstract

Disclosed is a nanopump for pumping small volumes of electrolyte solution under the control of a voltage source. The device includes a chamber and a nanopore membrane which partitions the chamber into upstream and downstream regions. When a voltage potential is applied across the membrane, electroosmotic flow through the membrane channels produces a precise-volume flow between the two chamber regions. Also disclosed is a method for precis-volume pumping employing the nanopump. Also disclosed is device for determining the lengths of nucleic acid fragments in an electrolyte solution of different-length fragments is disclosed. The device includes a chamber having disposed therein, a nanopore channel extending between upstream and downstream chamber regions. By applying a voltage potential across upstream and downstream electrodes in the chamber regions, individual nucleic acid fragments contained in the solution are moved through the channel. A current detector detects time-dependent current flow across said membrane, and from the measured flow times, fragments lengths can be estimated. Also disclosed is a device for separating macromolecules in a solution of macromolecules having different molecular sizes. The device includes a separation chamber having upstream and downstream ends, and one or more nanopore membranes disposed in the chamber between said upstream and downstream ends, partitioning the chamber into two or more chamber regions, respectively. Upstream and downstream electrodes are disposed at the upstream and downstream ends of the chamber, respectively. A controller in the device has a power source operatively connected to the electrodes for applying a selected voltage potential across said channel, to pump solution through each of said membranes, in an upstream-to-downstream direction, wherein macromolecules contained in the solution are filtered at each successive membrane, to concentrate successively smaller macromolecules in successively more downstream chamber regions.

What is claimed:  
     
         1 . A nanopump comprising 
 a supply reservoir for holding a supply electrolyte solution,    disposed against a wall region of the reservoir, a membrane having a plurality of flow-through channels extending between an inner membrane surface adapted for contact with said supply electrolyte solution, and an outer side adapted for contact with a recipient electrolyte solution contained outside of the supply reservoir, where said channels have a minimum cross-sectional dimension between 2 and 100 nm and a net surface charge when the pH of the supply solution is within a given pH range,    electrodes disposed on either side of membrane for contact with said supply and recipient solutions, and    a controller including a power source operatively connected to said electrodes for applying a selected voltage potential across said channel, to pump solution in the supply reservoir through said channel.    
     
     
         2 . The pump of  claim 1 , wherein said channels have a substantially uniform minimum dimension along their lengths.  
     
     
         3 . The pump of  claim 2 , wherein said channels have a minimum dimension in a selected range between about 2 and 30 nm.  
     
     
         4 . The pump of  claim 1 , wherein said controller is adapted to apply a voltage potential across the electrodes of between about 0.5-20 volts.  
     
     
         5 . The pump of  claim 4 , wherein said channels have a minimum dimension in a selected range between about 2 and 30, and application of a voltage potential across said electrodes of between about 0.5-20 volts is effective to produce a flow rate across said membrane of between about 0.25 and 1.25 ul/min.  
     
     
         6 . The pump of  claim 4 , wherein said controller includes a control element for applying across the electrodes a pulsed voltage whose duration is effective to pump a selected volume of supply solution across said membrane.  
     
     
         7 . The device of  claim 1 , wherein said membrane is formed of a silicon substrate with polysilicon and silicon dioxide layers.  
     
     
         8 . The pump of  claim 1 , which further includes a recipient reservoir designed for holding the recipient solution in contact with the outer side of said membrane.  
     
     
         9 . A method of pumping controlled and reproducible nanoliter quantities of an electrolyte solution from a supply reservoir into a recipient electrolyte solution comprising 
 placing the electrolyte solution in a supply reservoir, in contact with a membrane having a plurality of flow-through channels extending between an inner membrane surface adapted for contact with said supply electrolyte solution, and an outer membrane surface, said channels having a minimum cross-sectional dimension between 2 and 100 nm and a net surface charge at the pH of the supply solution,    placing the outer membrane surface in contact with a recipient electrolyte solution, and    with a pair of electrodes placed across said membrane, in contact with solution in said supply reservoir and with said recipient electrolyte, applying across said electrodes, a voltage potential effective to pump supply solution across said membrane from the supply reservoir into the recipient solution.    
     
     
         10 . The method of  claim 9 , wherein said channels have a substantially uniform minimum dimension along their lengths, and a minimum dimension in a selected range between about 2 and 30 nm.  
     
     
         11 . The method of  claim 10 , wherein the voltage potential applied across the membrane is between about 0.5 and 20 volts.  
     
     
         12 . The method of  claim 9 , wherein said recipient electrolyte solution is contained in a recipient reservoir, and said membrane is disposed between the supply and recipient reservoirs.  
     
     
         13 . A separation device for separating macromolecules in a solution of macromolecules having different molecular sizes, comprising 
 a separation chamber having upstream and downstream ends,    one or more membranes disposed in said chamber between said upstream and downstream ends, partitioning said chamber into two or more chamber regions, respectively, where (i) each membrane has a plurality of flow-through channels extending between adjacent chamber regions, (ii) said channels have a selected minimum cross-sectional dimension in the range between 2 and 100 nm and a net surface charge when exposed to a solution within a given pH range, and (iii) if the device contains two or more such membranes, the selected minimum cross-section of the channels in any membrane is greater than that in membrane immediately adjacent in the downstream direction,    upstream and downstream electrodes disposed in said chamber, for contacting solution placed in the chamber and contained in the in the upstream-most and downstream-most of the chamber regions, respectively, and    a controller including a power source operatively connected to said electrodes for applying a selected voltage potential across said channel, to pump solution through each of said membranes, in an upstream-to-downstream direction,    wherein macromolecules contained in said solution are filtered at each successive membrane, to concentrate successively smaller macromolecules in successively more downstream chamber regions.    
     
     
         14 . The device of  claim 13 , wherein said device contains at least two membranes, and at least two separate chamber regions.  
     
     
         15 . The device of  claim 14 , for use in separating globular proteins having solution radii between about 20 and 300 angstroms, wherein said membranes have selected sizes in the same range.  
     
     
         16 . The device of  claim 14 , which further includes a fluid outlet communicating with each chamber region, and an electrode associated with each outlet, and said voltage source is operably connected to said outlet electrodes, for diverting macromolecules in a chamber region out of the chamber through said outlet.  
     
     
         17 . The device of  claim 14 , wherein each chamber region has inlet and outlet ports for circulating liquid through that chamber, to remove separated macromolecules in the chamber region from the chamber,  
     
     
         18 . A method of separating macromolecules in a solution of macromolecules having different molecular sizes, comprising: 
 (a) placing the electrolyte solution in an upstream chamber region of a chamber having upstream and downstream chamber regions separated by a membrane having a plurality of flow-through channels extending between an inner membrane surface adapted for contact with said solution, and an outer membrane surface in contact with electrolyte solution contained in a downstream reservoir, where (i) said channels have a minimum selected cross-sectional dimension between 2 and 100 nm which is effective to block passage through the membrane of at least one of the different-sized macromolecules, and (ii) a net surface charge at the pH of said solution,    (b) with a pair of electrodes placed across said membrane, in contact with solution in said upstream and downstream reservoirs, applying across said electrodes, a voltage potential effective to pump supply solution across said membrane from the upstream into the downstream reservoir, wherein macromolecules in said solution are separated on the basis of their ability to pass through the channels in said membrane.    
     
     
         19 . The method of  claim 18 , wherein said chamber includes at least two membranes, at least three separate chamber regions, and the selected minimum cross-section of the channels in any membrane is greater than that in the membrane immediately downstream.  
     
     
         20 . The method of  claim 19 , which further includes periodically removing macromolecules accumulated in each of said chamber regions.  
     
     
         21 . A device for determining the lengths of nucleic acid fragments in an electrolyte solution of different-length fragments and having a selected pH, comprising 
 a chamber,    a membrane disposed in said chamber and having a channel extending between an upstream chamber region adapted to hold the electrolyte solution of such different-length fragments, and a downstream chamber region adapted to hold an electrolyte solution, where (i) said channel has a selected minimum cross-sectional dimension in the range between 2 and 15 nm and a net surface charge within a given pH range that includes the selected solution pH,    upstream and downstream electrodes disposed in said upstream and downstream chamber regions, respectively, for contacting solution placed in the corresponding chamber regions,    a controller including (i) a power source operatively connected to said electrodes for applying a selected voltage potential across said channel, to move individual nucleic acid fragments contained in the solution through said channel, and (ii) a current detector for detecting time-dependent current flow across said membrane.    
     
     
         22 . The device of  claim 21 , wherein said channel is formed by a pair of planar channels, each having a channel thickness in the 2-20 nm range, arranged orthogonally with respect to one another, such that the intersection of the two channels a forms a rectangular area whose dimensions correspond to the two thicknesses of the intersecting channels.  
     
     
         23 . The device of  claim 21 , wherein said membrane has a plurality of channels, and said current detector is effective to measure time-dependent current independently through each of said channels.  
     
     
         24 . The device of  claim 21 , wherein said minimum channel width is within the range 2-10 nm.  
     
     
         25 . The device of  claim 21 , wherein said controller is effective to place across the electrodes, a voltage potential effective to move nucleic acid fragments electrophoretically through said channel.  
     
     
         26 . A method for determining the lengths of nucleic acid fragments in an electrolyte solution of different-length fragments and having a selected pH, comprising 
 (a) placing the solution in an upstream chamber region of a chamber having upstream and downstream chamber regions separated by a membrane having a channel extending between the two chamber regions, where (i) said channel has a selected minimum cross-sectional dimension in the range between 2 and 15 nm and a net surface charge within a given pH range that includes the selected solution pH,    (b) with a pair of electrodes placed across said membrane, in contact with solution in said upstream and downstream chamber regions, applying across said electrodes, a voltage potential effective to pump solution across said channel, wherein individual nucleic acid fragments move through said channel, and    (c) detecting time-dependent changes in current flow through said channel, as a measure of the length of individual nucleic acid fragments moving through said channel.    
     
     
         27 . The method of  claim 26 , wherein said membrane has a plurality of channels, and said detecting includes detecting time-dependent changes in current flow separately through each of said channels.  
     
     
         28 . The method of  claim 26 , wherein said minimum channel width is within the range 2-10 nm.